The present invention relates to systems and methods for treating process material and, more particularly, to systems and methods for treating municipal solid waste material, medical waste material, reclaimed paper and the like.
As a result of increasing scarcity of landfills and more stringent environmental regulations, efforts have been made to reduce the volume of process material, such as municipal solid waste (“MSW”) and paper material, such as newsprint and other reclaimed and recycled paper products as a step in the process of disposing of the material, either by depositing it in landfills, incinerating it or recycling it.
Systems and methods have been developed to break down such material for disposal, or in the case of paper products, use as insulation.
An example of such a process and device is U.S. Pat. No. 5,190,226, which discloses an apparatus and method for separation, recovery and recycling of MSW. The apparatus includes a rotating drum which is fed at an upstream end by a reciprocating ram, a steam source which is connected to introduce high temperature steam into the drum, and a spiral rib or flight mounted within the drum to transport material deposited in an upstream end of the drum along the length of the drum.
Another example is described in U.S. Pat. No. 5,119,994 that describes a steam treatment vessel held stationary, preferably at an angle to the horizontal.
One of the disadvantages of the arrangements of the prior art is that portions of the waste product charge in the vessel become compacted, either passively by maintaining the vessel at a fixed position with respect to the horizontal, or actively through the use of spiral or helical rib arrangements that urge portions of the charge against active surfaces in a horizontal direction (or a direction parallel to the longitudinal axis of the vessel) as the vessel is rotated. In some instances, the compacted portions of the waste product charge cause portions of the waste product charge to be sequestered from the steam treatment environment.
Another disadvantage of the prior art is that prior systems and methods do not allow for the most advantageous control and distribution of energy placed into the vessel, and its efficient transfer to the waste charge mass. In addition, each charge of waste products will vary in its constituents, and thereby in its heat capacity and in its energy requirements for effective treatment. In methods of the prior art, either the process parameters (temperature, pressure, or time) had to be varied with each charge of waste, or the consistency of the processed product (i.e., particle size, moisture content, degree of break down and processing generally) varied with batch to batch. This made an economically and technically viable industrial process for the treatment of waste less than efficient.
Accordingly, it is also advantageous to be able to determine the heat capacity of a given charge of waste products thereby to determine the energy requirements for effective treatment of that charge, in order treatment can be carried out with higher efficiency.
One method of attempting to reach achieve more efficient treatment is described in U.S. Pat. No. 6,397,492 and involves the continual supply of steam during loading, while simultaneously rotating the vessel, so as to break down the waste during loading to a material of roughly uniform density, so that the same mass of waste is processed in each batch. However, this process requires a separate steam treatment during loading which results in greater overall time requirements for each waste batch.
Accordingly, there remains a need for methods that allow for greater time and energy efficiency while allowing the process of waste in charges that vary in weight and constituents.
In addition, it is also desirable to be able to reduce the amount of water in the processed waste mass to make it amenable for further processing into fuel pellets. As excess water typically must be removed by active drying, this requires additional time and energy investment. Accordingly, another aspect of the present invention addresses the need to efficiently remove excess water, especially that in the interstitial spaces of the waste material mass.
The present invention accordingly represents an improvement over prior art apparatus and methods, such as those described in U.S. Pat. Nos. 5,540,391; 5,116,363; 5,253,764; 5,190,226; 5,361,994; 5,427,650; 5,407,809; and 6,397,492, and in published European Patent Application No. 02758620.5; all of which are incorporated herein by reference. The present invention also represents an improvement over co-pending application Ser. No. 11/122,341, which is hereby incorporated by reference.